1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic device, an electrostatic recording device and the like, a process cartridge mountable to such image forming apparatus, and an image bearing member such as a photosensitive drum, a dielectric drum and the like used with such apparatus.
2. Related Background Art
In image forming apparatuses such as copying machines, a latent image is formed by selectively exposing an image bearing member which has been uniformly charged, and the latent image is then visualized with toner as a toner image which is in turn transferred onto a recording sheet, thereby recording an image on the recording sheet. In such apparatuses, whenever the toner is consumed or used up, new toner must be replenished. However, the toner replenishing operation not only is troublesome, but also often causes the contamination of surroundings. Further, the maintenance of various elements must be performed only by expert servicemen, which is inconvenient for the user.
To avoid this, a so-called process cartridge wherein a photosensitive drum, a charger, a developing device, a cleaning device and the like are integrally contained in a cartridge housing which can be removably mounted to an image forming apparatus, whereby the replenishment of toner or the exchange of parts the service lives of which have been expired can be permitted and maintenance can be facilitated, and an image forming apparatus to which such process cartridge can be mounted have been proposed and put into practical use.
As charger devices used with such image forming apparatus such as an electrophotographic device, in general, a corona discharger has been conventionally utilized. However, recently, since a power source of low voltage type has been developed, a charger of contact type having a roller-shaped or blade-shaped conductive member has been used because of low generation of ozone. In such a charger, when an AC voltage is applied to the charger roller, the photosensitive drum and the charger roller are vibrated at a frequency twice as great as the frequency of the applied AC voltage, thereby generating charging noise.
On the other hand, in order to keep the base potential of the image bearing member constant, the image bearing member is electrically earthed by abutting an elastic drum earth against the image bearing member. However, since the drum earth cannot follow the vibration of the image bearing member sufficiently, it is feared that weak vibrating noise due to the vibration of the drum earth is generated between the image bearing member and the drum earth. To avoid this, it is considered that a contacting pressure between the drum earth and the image bearing member is increased. However, if such contact pressure is too great, the inner surface of the drum is damaged due to the strong abutment between the drum and the drum earth for a long time, with the result that, whenever a contact portion of the drum earth passes through the damaged portion of the drum, the poor contact and the vibrating noise will be generated.